Stripping agent composition and method of stripping

ABSTRACT

A stripping composition comprising (a) an anticorrosive agent, (b) a stripping agent and (c) a solvent, wherein the anticorrosive agent (a) is a heterocyclic compound having a nitrogen atom-containing six-membered ring.

TECHNICAL FIELD

The present invention relates to a stripping composition used forremoving unnecessary substances remaining on a semiconductor substratein the process for production of semiconductor device, for example, aresist film and an etching residue both remaining after dry etching ofinsulating film, as well as to a stripping method.

BACKGROUND ART

The steps for forming throughholes, wiring grooves, etc., employed inthe process for production of semiconductor device are conducted usinglithography. They are conducted ordinarily by forming a resist film,then conducting dry etching using the resist film as a mask, and thenremoving the resist film. Here, the removal of the resist film isconducted generally by plasma ashing and subsequent wet treatment usinga stripping solution. As the stripping solution, various solutions haveheretofore been developed and there are known, for example, organicsulfonic acid-based stripping solutions containing analkylbenzenesulfonic acid as the main component, organic amine-basedstripping solutions containing an amine (e.g. monoethanolamine) as themain component, and hydrofluoric acid-based stripping solutionscontaining hydrofluoric acid or a salt thereof as the main component.

Meanwhile, in recent years, low-resistance wiring materials such ascopper have come to be used in response to the higher speed required forsemiconductor elements, and it has become necessary that strippingsolutions have anticorrosivity for wiring materials. The reason is thatcopper, as compared with conventional wiring materials such as aluminum,is inferior in anticorrosivity to stripping solutions and tends tocorrode during a stripping step.

As a technique for preventing a metal film formed on a semiconductorsubstrate, from corroding, there is disclosed, in JP-A-7-247498, atechnique for preventing corrosion of aluminum alloy by using, forcleaning after ashing, an aqueous solution containing a quaternaryammonium hydroxide, a saccharide or a sugar alcohol, and a ureacompound. In this document is shown specifically a cleaning solutioncomprising tetramethylammonium hydroxide, sorbitol, urea and water. Whena wiring is formed using an aluminum alloy film composed mainly ofaluminum, steps are taken which comprise forming a photoresist ofpredetermined pattern on an aluminum alloy film and then dry-etching thealuminum alloy film using the photoresist as a mask. After thedry-etching, there is formed, on the side wall of the aluminum alloyfilm, a side wall-protecting film which is a product of reaction betweenthe photoresist and the dry etching gas used. In this case, since achlorine-based gas is generally used as the dry etching gas, there hasbeen a problem that chlorine is taken into the side wall-protecting filmand the aluminum alloy film is corroded after the completion of theetching. In the technique disclosed in JP-A-7-247498, it is describedthat the side wall-protecting film containing chlorine can be removedeffectively by using a cleaning solution having the above-mentionedparticular composition. This technique is intended to efficiently removethe chlorine-containing side wall-protecting film (which causescorrosion of aluminum alloy film) and improve the stripping performanceof resist-stripping solution; however, the technique does not provide ananticorrosive agent which is effective for corrodible metals such ashigh-purity copper.

Meanwhile, a resist-stripping solution used for anticorrosion andcleaning of metal is disclosed in, for example, JP-A-8-334905. In thisdocument, there are shown, as examples of anticorrosive agent, aromatichydroxy compounds such as catechol, pyrogallol and hydroxybenzoic acidand carboxyl group-containing organic compounds such as acetic acid,citric acid and succinic acid. These anticorrosive agents, however, areintended to prevent corrosion of aluminum-copper alloys composed mainlyof aluminum and have no sufficient anticorrosivity for high-puritycopper of high corrodibility. In the above JP-A-8-334905 are disclosed,as other anticorrosive agents, benztriazole (BTA) and derivativesthereof. When this anticorrosive agent is used, certain anticorrosivityis obtained even to corrodible metals like copper.

BTA and derivatives thereof, however, are difficult to subject tobiodegradation and the treatment of a waste solution containing them hasbeen difficult. In recent years, a requirement for lower environmentalload has become strong and higher safety has become necessary also forchemical substances used in factories producing semiconductor devices.Organic wastewaters generated in the factories are generally subjectedto a biological treatment and, after decomposition, are discharged.Regarding substances incapable of being subjected to any biologicaltreatment, it is desired to treat them using other means or change themto other chemical substance showing biodegradability. Theabove-mentioned TBA or derivatives thereof are extremely difficult tosubject to the biological treatment. For the above reasons, in thefactories using a stripping solution containing BTA or a derivativethereof, the waste solution or wastewater generated has had to betreated at a high environmental risk or by a method other thanbiodegradation, requiring a high cost and much labor.

In JP-A-9-291381 is described a conventional technique different fromthe present invention, that is, effectiveness of a urea condensationproduct as a water-soluble rust preventive. As examples of the ureacondensation product, there are shown isocyanuric acid, hydantoin, uricacid, triscarboxymethylisocyanuric acid and triscarboxyethylisocyanuricacid. This technique, however, aims at rust prevention of metal duringmetal processing (e.g. cutting, polishing and plastic processing) andstorage of worked metal and is not intended to provide a technique forremoval of residue remaining in very fine holes and high-level surfacecleaning, such as required in semiconductor device production. Further,the technique described in the above document aims at rust prevention ofmetal and has a task different from that (“anticorrosion”) of thepresent invention.

“Rust prevention” is to prevent the progress of oxidation of metal. Incontrast, the “anticorrosion” aimed at in the present invention is toprevent corrosion of a metal film formed on a semiconductor wafer,specifically to prevent dissolution of metal (e.g. copper) or formationof metal complex, using a stripping component contained inresist-stripping solution. Treatment by rust preventive is conductedordinarily in air and forms a protective layer made of rust preventive,on an oxide film present on a metal. In contrast, the “anticorrosion” ofthe present invention forms a protective layer on a clean metal surfacenot oxidized, by allowing an anticorrosive agent to act on the surface.A metal film formed on a semiconductor wafer, even when the surface hasbeen oxidized (i.e. rusted) slightly, produces various problems such asincreased resistance, insufficient adhesion with a film formed thereon,and the like. Therefore, the anticorrosive agent of the presentinvention is required to form a dense protective film on a metal filmfor substantially complete prevention of the oxidation of the metal filmand further for effective prevention of the dissolution of the metalfilm and the formation of a metal complex both caused by aresist-stripping solution or a cleaning solution. That is, in the“anticorrosion” of the present invention is required a high-degree ofmetal film protectability rather than rust prevention. Further, asdescribed later, the anticorrosive agent used in resist-strippingcomposition, unlike ordinary anticorrosive agents for metal members, isneeded to have various properties. Thus, in designing a resist-strippingcomposition used in production of semiconductor device, an investigationmust be made from standpoints different from those required in ordinaryrust prevention of metals.

DISCLOSURE OF THE INVENTION

The present invention has been made in consideration of the abovesituation and aims at providing a stripping composition which caneffectively remove a resist film and an etching residue while preventingthe corrosion of a corrodible metal such as copper and which is superiorin product safety, is subjectable to a biological treatment and is easyto treat its wastewater.

Development of an anticorrosive agent used in a resist-strippingsolution has been made mainly for improvement of anticorrosivity towiring material. In order to further consider lower environmental risksuch as safety and biodegradability, an investigation based onstandpoints different from conventional standpoints is needed. Thepresent inventors made an investigation from such standpoints and foundout that heterocyclic compounds having a particular structure have goodanticorrosivity. The finding has led to the completion of the presentinvention.

According to the present invention there is provided a strippingcomposition comprising (a) an anticorrosive agent, (b) a stripping agentand (c) a solvent, wherein the anticorrosive agent (a) is a heterocycliccompound having a nitrogen atom-containing six-membered ring.

According to the present invention there is also provided a strippingcomposition comprising (a) an anticorrosive agent, (b) a stripping agentand (c) a solvent, wherein the anticorrosive agent (a) is a heterocycliccompound having a five- or six-membered heterocyclic ring containing anatomic group of —C(OH)═N— or —CONH—.

According to the present invention there is also provided a strippingcomposition comprising (a) an anticorrosive agent, (b) a stripping agentand (c) a solvent, wherein the anticorrosive agent (a) is purine or aderivative thereof.

According to the present invention there is also provided a strippingcomposition comprising (a) an anticorrosive agent, (b) a stripping agentand (c) a solvent, wherein the anticorrosive agent (a) is a compoundrepresented by the following general formula (1):

wherein A₁, A₂ and A₃ are each independently a hydrogen atom, a hydroxylgroup, an alkyl group having 1 to 5 carbon atoms or an amino group.

According to the present invention there is provided a stripping methodwhich comprises removing a resist film and/or an etching residue,present on a semiconductor substrate containing an exposed metal filmsurface, using the above-mentioned stripping composition.

According to the present invention there is also provided a strippingmethod which comprises forming a metal film and an insulating film on asemiconductor wafer in this order, forming a resist film thereon,conducting dry etching using the resist film as a mask, to form, in theinsulating film, a hollow reaching the metal film, and removing theresist film and/or a reside of etching, wherein the removal is conductedusing the above-mentioned stripping composition.

According to the present invention there is also provided a strippingmethod which comprises forming, on a semiconductor wafer, a metal film,a first insulating film and a second insulating film having apredetermined opening in this order, conducting dry etching using thesecond insulating film as a mask, to form, in the first insulating film,a hollow reaching the metal film, and removing a residue of etching,wherein the removal is conducted using the above-mentioned strippingcomposition.

In the above stripping methods, the metal film can be a film made of,for example, copper or a copper alloy.

In the present invention, there is used, as the anticorrosive agent, aheterocyclic compound having a particular structure, such as mentionedabove; therefore, a dense protecting layer is formed on a metal film andexcellent anticorrosivity is exhibited. Further, the compound issuperior in product safety and has biodegradability, making itswastewater treatment easy.

The stripping composition of the present invention is used, mainly inproduction of semiconductor device, for removal of a resist film and aresidue thereof and also for removal of, for example, a residueremaining after an interlayer dielectric has been etched without forminga resist film.

In the present invention, the anticorrosive agent is used as a componentof the stripping composition and, therefore, unlike ordinaryanticorrosive agents for metal members, need to have various properties.

Firstly, in production of semiconductor device, since the propertiesintended in designing are often unobtainable even when part of the metalwiring has been damaged slightly, the anticorrosive agent used needs tohave very high-level anticorrosivity. In addition, such high-levelstripping performance need be exhibited in coexistence of a strippingcomponent such as amine or hydrofluoric acid salt.

Secondly, the anticorrosive agent used needs to give no damage to asemiconductor substrate and various films formed thereon. In recentproduction of semiconductor device, chips are becoming increasinglyfiner and, even when the substrate and films constituting asemiconductor device have been damaged slightly, the properties of chipsmay be damaged decisively.

Thirdly, the anticorrosive agent needs to give no adverse effect in thesteps conducted after a stripping treatment. For example, when aninsulating film or other metal film is formed on a metal film havingthereon a remaining anticorrosive agent, properties of chips may beadversely affected owing to increased resistance, film stripping, etc.Therefore, it is desired to select such an anticorrosive agent as toshow no adverse effect on chip properties even when remaining or to bedetached from a metal film after an anticorrosive treatment but beforeproceeding to the nest step.

Fourthly, since the anticorrosive agent is used in production ofsemiconductor device, the amount of its waste solution is large and thetreatment thereof need be conducted, in particular, safely rapidly andat a low cost. Therefore, it is strongly required that the anticorrosiveagent is constituted by biodegradable components.

The anticorrosive agent contained in the stripping composition of thepresent invention has all the above properties. That is, theanticorrosive agent contained in the stripping composition of thepresent invention exhibits high anticorrosivity even under thecoexistence of a stripping agent and gives no damage to substrate orother films. Further, the anticorrosive agent adhering to a metal filmcan be quickly detached by, for example, preheating for film formation.Furthermore, the present anticorrosive agent is superior in safety andbiodegradability.

BRIEF DESCRIPTION OF THE DRAWINGS

FIGS. 1(a)-1(c) are sectional views explaining steps for throughholeformation process.

FIGS. 2(a)-2(d) are sectional views explaining steps for throughholeformation process.

FIG. 3 is a graph showing an effect of uric acid concentration onetching rate of copper film.

BEST MODE FOR CARRYING OUT THE INVENTION

In the present invention, the component (a) contains a heterocycliccompound having a nitrogen atom-containing six-membered ring in themolecule. Such a heterocyclic compound exhibits good anticorrosivityowing to the chelating action expressed by the nitrogen atom present inthe heterocyclic ring and also has good biodegradability.

When there is used, as the component (a), a heterocyclic compound havinga five- or six-membered heterocylic ring containing an atomic group of—C(OH)═N— or —CONH—, the compound exhibits particularly goodanticorrosivity and biodegradability. The reason is not clear but ispresumed to be as follows:

In the above heterocyclic compound, C, N, O and H are on the same plane;therefore, —C(OH)═N— (amide unit) and —CONH— (iminohydrin unit) showtautomerism. This is known as lactam-lactim tautomerism (the followingformula).

In the above formula, a conjugated system is formed on N, C and O atomsand, electrons are delocalized at this conjugated region. Since theelectrons in the conjugated system tend to interact with the emptyorbits on a metal surface, it is considered that a stable chelate bondis formed.

Further, since the above atomic group is contained in the ring portionof the five- or six-membered heterocyclic ring, it is considered thatthe heterocyclic compound is low in steric hindrance, the above atomicgroup tends to approach metal atoms, and a chelate bond is easilyformed.

Striking anticorrosivity shown by a heterocyclic compound having, in themolecule, a five- or six-membered heterocyclic ring containing amideunit or iminohydrin unit is presumed to be due to the above reason.

Also, good biodegradability shown by the above compound is presumed tobe associated with the high bioaffinity of amide bond.

In the present invention, specific examples of the heterocyclic compoundinclude purine and its derivatives, such as purine, 6-aminopurine,2-amino-6-oxopurine, 6-furfurylaminopurine, 2,6-(1H,3H)-purinedione,2-amino-6-hydroxy-8-mercaptopurine, alloplinol, uric acid, kinetin,zeatin, guanine, xanthine, hypoxanthine, adenine, theophylline, caffeineand theobromine; azaguanine and its derivatives, such as 8-azaguanine;pteridine, pterin and their derivatives, such as pteridine, pterin,2-amino-4,6-dihydroxypteridine, 2-amino-4,7-dihydroxypteridine and2-amino-4,6,7-trihydroxypteridine; cyanuric acid, isocyanuric acid andtheir derivatives, such as cyanuric acid, isocyanuric acid,triscarboxymethylcyanuric acid, triscarboxyethylcyanuric acid,triscarboxymethylisocyanuric acid and triscarboxyethylisocyanuric acid;hydantoin, allantoin and their derivatives, such as hydantoin,dimethylhydantoin and allantoin (5-ureidohydantoin); barbituric acid andits derivatives; and nicotinic acid and its derivatives, such asisonicotinic acid and citrazinic acid. These compounds can be usedsingly or in combination of two or more kinds. Of these, purine and itsderivatives, and nicotinic acid and its derivatives are used preferably.The reason is that they are superior in biodegradability and moreoverexhibit excellent anticorrosivity to metals such as copper.

Of the above compounds, purine and its derivatives, in particular, areused preferably because they exhibit excellent anticorrosivity to metalssuch as copper even in the coexistence of a stripping component such asamine and hydrofluoric acid salt, gives no damage to a semiconductorsubstrate and various films formed thereon, and gives no adverse effecton steps conducted after a stripping treatment. Especially, thecompounds represented by the following general formula (1), mostespecially, uric acid is used preferably because it is a substance ofhigh safety widely present in nature, is particularly superior inbiodegradability and has strikingly excellent anticorrosivity.

wherein A₁, A₂ and A₃ are each independently a hydrogen atom, a hydroxylgroup, an alkyl group having 1 to 5 carbon atoms or an amino group. Inthe above formula, at least either of A₂ and A₃ is desirably a hydroxylgroup. Thereby, the heterocycle has an amide bond therein and very goodanticorrosivity and biodegradability are obtained.

Incidentally, it is known that in the compound having an amide unit inthe cyclic portion, the amide unit is converted into an iminohydrin unitand tautomerism holds between lactam form and lactim form as shown inthe following formula. Uric acid, for example, takes the followingresonance structure.

In the present invention, the lower limit of the amount of the component(a) is preferably 0.0001% by weight, more preferably 0.001% by weight.With such an amount, very good anticorrosivity is obtained. The upperlimit is not critical but is, for example, about 20% by weight,preferably about 10% by weight in view of the solubility of component(a) in stripping solution. Incidentally, in the present specification,the amount of each component is based on the total stripping compositionunless otherwise specified.

In the present invention, there can be used, as the component (b), analkanolamine or a hydrofluoric acid salt.

As specific examples of the alkanolamine, there can be shownmonoethanolamine, diethanolamine, N-ethylaminoethanol,N-methylaminoethanol, N-methyldiethanolamine, dimethylaminoethanol,2-(2-aminoethoxy)ethanol, 1-amino-2-propanol, triethanolamine,monopropanolamine and dibutanolamine. Of these, monoethanolamine andN-methylaminoethanol are particularly preferred.

Alkanolamines such as monoethanolamine, and N-methylaminoethanol showgood biodegradability; therefore, when such a compound is selected as astripping agent component, the resulting stripping composition of thepresent invention can have higher safety and biodegradability.

A hydrofluoric acid salt can be used as the component (b) when aresidue, etc. difficult to remove with an amine type stripping componentis removed. Specifically, ammonium fluoride, etc. are used preferably.With a hydrofluoric acid salt, a deposit, etc. adhering to a resistsidewall can be removed.

In the present invention, the upper limit of the amount of the component(b) is preferably 95% by weight, particularly preferably 85% by weight.The lower limit is preferably 1% by weight, particularly preferably 10%by weight. With such an amount, a resist film and an etching residue canbe removed very efficiently while good anticorrosivity is maintained.

In the present invention, water can be used as the component (c).

In the present invention, the upper limit of the amount of the component(c) is preferably 90% by weight, particularly preferably 80% by weight.The lower limit is preferably 1% by weight, particularly preferably 5%by weight. With such an amount, the dissolution of the anticorrosiveagent is promoted, good anticorrosivity is maintained, and a resist filmand an etching residue can be removed very efficiently.

In the present invention, the component (c) may contain a water-solubleorganic solvent. As the water-soluble organic solvent, there can be usedan organic solvent miscible with water and other components of thepresent invention.

As such a water-soluble organic solvent, there can be mentionedsulfoxides such as dimethyl sulfoxide; sulfones such as dimethylsulfone,diethylsulfone, bis(2-hydroxyethyl)sulfone and tetramethylenesulfone;amides such as N,N-dimethylformamide, N-methylformamide,N,N-dimethylacetamide, N-methylacetamide and N,N-diethylacetamide;lactams such as N-methyl-2-pyrrolidone, N-ethyl-2-pyrrolidone,N-propyl-2-pyrrolidone, N-hydroxymethyl-2-pyrrolidone andN-hydroxyethyl-2-pyrrolidone; imidazolidinones such as1,3-dimethyl-2-imidazolidinone, 1,3-diethyl-2-imidazolidinone and1,3-diispropyl-2-imidazolidinone; lactones such as γ-butyrolactone andδ-valerolactone; and polyhydric alcohols and their derivatives, such asethylene glycol, ethylene glycol monomethyl ether, ethylene glycolmonoethyl ether, ethylene glycol monobutyl ether, ethylene glycolmonomethyl ether acetate, ethylene glycol monoethyl ether acetate,diethylene glycol, diethylene glycol monomethyl ether, diethylene glycolmonoethyl ether and diethylene glycol monobutyl ether. These solventsmay be used singly or in combination of two or more kinds. Of these,preferred are dimethyl sulfoxide, N,N-dimethylformamide,N,N-dimethylacetamide, N-methyl-2-pyrrolidone,1,3-dimethyl-2-imidazolidinone, ethylene glycol and diethylene glycolmonobutyl ether, for their excellent stripping ability. Particularlypreferred is N-methyl-2-pyrrolidone because it is superior also inanticorrosivity to substrate.

The stripping composition of the present invention may comprise only thecomponents (a) to (c) but may further contain other components asnecessary unless the characteristics of the present invention are notimpaired.

The stripping composition of the present invention can be used forstripping of various resists and can be applied to resists for KrF, madeof an aromatic compound, as well as to resists for ArF, made of analicyclic acrylic polymer or the like. The present stripping compositioncan be used to, for example, (i) a positive resist containing anaphthoquinone diazide compound and a novolac resin, (ii) a positiveresist containing a compound which generates an acid when exposed to alight, a compound which is decomposed by the acid to have an increasedsolubility in an aqueous alkali solution, and an alkali-soluble resin,(iii) a positive resist containing a compound which generates an acidwhen exposed to a light and an alkali-soluble resin having a group whichis decomposed by the acid to have an increased solubility in an aqueousalkali solution, and (iv) a negative resist containing a compound whichgenerates an acid when exposed to a light, a crosslinking agent and analkali-soluble resin.

The stripping composition of the present invention aims at removingunnecessary substances present on a semiconductor substrate. Theunnecessary substances present on a semiconductor substrate refer tovarious unnecessary substances produced during production ofsemiconductor device and include a resist film, an etching residue afterdry etching, a chemically modified resist, etc. The present strippingcomposition is very effective when the substances to be stripped orremoved are a resist film and/or an etching residue present on asemiconductor substrate containing an exposed surface of a metal film.When the above metal film is a copper film, the stripping composition ofthe present invention exhibits anticorrosivity more effectively.

The present invention, when applied to a process using, as an interlayerdielectric material, a low dielectric constant material, for example, apolyorganosiloxane such as MSQ (methylsilsesquioxane), HSQ(hydrogensilsesquioxane) and MHSQ (methylated hydrogensilsesquioxane),or an aromatic-containing organic material such as polyaryl ether (PAE)and divinylsiloxane-bis-benzocyclobutene (BCB), is effective in that thefilm made of such a material is damaged at a lower extent. These lowdielectric constant materials are often utilized as an interlayerdielectric for reduction in capacity between neighboring wirings;however, they have had a problem of low ashing resistance and, whensubjected to plasma, increased dielectric constant. Therefore, it isdesired to make the time of ashing as short as possible and theconditions of ashing as mild as possible. This makes essential atreatment using a stripping solution having a strong stripping action.Such a stripping component of strong stripping action, however,inevitably shows a strong corrosivity to wiring materials such ascopper; therefore, an anticorrosive component stronger than before isneeded. Thus, in a process using the above-mentioned low dielectricconstant material, the present invention exhibits its effect morestrikingly.

The present invention is effective when applied to a resist film and/oran etching residue both present on a semiconductor wafer containing anexposed surface of a metal film, and particularly effective when themetal film is made of copper or a copper alloy made mainly of copper.The copper alloy made mainly of copper is a copper alloy containingcopper in an amount of 90% by weight or more and other elements such asMg, Sc, Zr, Hf, Nb, Ta, Cr, and Mo. These metals have low resistancesand increase the high-speed operability of chip but tend to showcorrosion (dissolution, modification, etc.) when exposed to a chemicalsolution; therefore, the present invention shows a striking effect tothese metals.

Next, there is shown, as an application example of the strippingcomposition of the present invention, a case of forming a interlayercontact plug on copper wiring by a single damascene process.

First, as shown in FIG. 1(a), on a semiconductor substrate (not shown)having elements such as transistor, formed thereon are formed a siliconoxide film 1, a silicon nitride film 2 and a silicon oxide film 3. Then,a copper wiring consisting of a barrier metal film 4 and a copper film 5is formed using a known damascene process utilizing chemical mechanicalpolishing (CMP). Thereon are formed a silicon nitride film 6 having athickness of about 50 to 100 nm and an interlayer dielectric (a siliconoxide film or a low dielectric constant film) 7 having a thickness ofabout 600 to 1,000 nm. The thickness of the copper film 5 can beselected as desired, but is preferably set at, for example, 350 nm orless for a lower parasitic capacity between neighboring wirings. Whenthe thickness of the copper wiring is small, the thickness of thecorroded layer relative to the total copper wiring layer becomesrelatively large and an increase in wiring resistance, caused by thecorrosion of copper surface becomes a big problem; however, with thestripping composition of the present invention, such a problem is solvedand the thickness of the copper wiring layer can be made small.Incidentally, in the present embodiment, the thickness of the siliconnitride film 6 is set at about 50 to 100 nm; however, the thickness maybe larger than that to enhance the function as an etching-preventingfilm.

Next, on the interlayer dielectric film 7 is provided a resist film 8 ina predetermined pattern [FIG. 1(b)].

Next, the interlayer dielectric film 7 is dry-etched using the resistfilm 8 as a mask, until the silicon nitride film 6 is exposed, whereby athroughhole 10 is formed [FIG. 1(c)]. At this time, an etching residue11 adheres to the inner wall of the throughhole 10. The diameter of thethroughhole is set at about 0.2 μm. The etching gas used is preferably agas capable of etching the interlayer dielectric film at a largeretching rate than etching the silicon nitride film.

Here, the silicon nitride film 6 has a function for prevention of copperdiffusion and, besides, a function as an etching-stopper film; however,as shown in FIG. 1(c), the controlled stoppage of dry etching on thesilicon nitride film 6 is impossible in some cases. The reason is asfollows: In a process such as the present embodiment, throughholes ofvarious diameters are generally formed on a semiconductor wafer. Inthroughholes of small diameters, the rate of etching is small owing to amicroloading effect. Hence, it becomes necessary to take a certainoveretching time in the etching for throughholes formation; as a result,the silicon nitride film 6 is etched in part of the throughholes andpart of the copper film 5 is exposed. Further, when a hollow appears(dishing) on, for example, the copper film 5, the silicon nitride film 6generates a thin film portion and is etched at this portion, which mayresult in exposure of part of the copper film 5. This exposure of thecopper film 5 can be prevented by forming a silicon nitride film 6 oflarge thickness in the step shown in FIG. 1(a); in this case, however,the capacity between neighbonng copper wirings becomes large and thehigh-speed operation of semiconductor elements tends to be hindered.

After the completion of the etching, part of the resist film 8 isremoved by oxygen plasma ashing, after which a stripping treatment isconducted using the stripping composition of the present invention. Bythis stripping treatment, the resist film and the etching residue 11,which have not been removed sufficiently in the ashing, are removed. Asdescribed above, the copper film 5 is exposed in at least part of thethroughholes, after the etching; therefore, the stripping compositionneeds to have anticorrosivity to copper. By using a strippingcomposition containing the above-mentioned components (a) and (b), theresist film and the etching residue 11 can be removed effectivelywithout any damage to the copper film 5. A state after the completion ofthe stripping treatment is shown in FIG. 2(a).

Then, etching of the silicon nitride film 6 is conducted by changingetching gas. At this time, an etching residue 12 adheres to the innerwall of the throughhole 10 [FIG. 2(b)]. In order to remove the etchingresidue 12, a stripping treatment is conducted again using theabove-mentioned stripping composition. At this stage of strippingtreatment, the copper film 5 is exposed at the bottom of the throughhole10; however, use of the stripping composition containing the components(a) and (b) allows removal of the etching residue 12 without giving anydamage to the copper film 5 [FIG. 2(c)].

Then, inside the throughhole are formed a barrier metal film 14 (whichconsists of a Ti layer and a TiN layer in this order) and a tungstenfilm 15, after which CMP is conducted for planarizing, to form aninterlayer contact plug [FIG. 2(d)].

EXAMPLE 1

Stripping compositions of the present invention were applied to stepsfor throughhole formation on a copper wiring, for evaluation of theirstripping performances and anticorrosivity.

Samples to be examined were produced according to the same steps asshown in FIG. 1 to FIG. 2(c). First, a copper wiring was formed on asilicon wafer; thereon were formed a silicon nitride film having athickness of 90 nm and an interlayer dielectric film (HSQ or MSQ) havinga thickness of 900 nm. Then, a positive resist film was formed byspinner coating. As the material for the resist film, there was used“PEX 4” (produced by Tokyo Ohka Kogyo Co., Ltd.) which was a materialfor positive resist for KrF). The resist film was exposed to a light viaa mask pattern and subjected to development using an aqueoustetramethylammonium hydroxide solution to obtain a resist pattern.

Using this resist film as a mask, the interlayer dielectric film wasdry-etched until the silicon nitride film was exposed, to form athroughhole having a diameter of 0.2 μm. As the gas for etching, afluorocarbon-based gas was used. After the completion of the etching,part of the resist film was removed by oxygen plasma ashing, after whicha stripping treatment was conducted using a stripping composition shownas No. 1 in Table 1.

Next, the silicon nitride film was etched using a different etching gas,to expose the copper wiring at the bottom of the throughhole. In orderto remove the residue generated by this etching, a stripping treatmentwas conducted again using the same stripping composition (No. 1 inTable 1) as used in the previous stripping treatment.

The same operation was conducted for stripping compositions Nos. 2 to 17shown in Table 1, to produce total 17 kinds of samples.

The wafers after the above treatment were rinsed with pure water andthen subjected to sectional observation using a scanning electronmicroscope (SEM) to evaluate (1) stripping performance of resist filmand etching resist and (2) anticorrosivity to copper film. The standardfor evaluation was as follows:

(Stripping Performance)

The residual conditions of resist film and etching residue were observedand rated according to the following four stages:

⊚: There was no residue.

◯: There was substantially no residue.

Δ: There was a small amount of residue.

X: There was a large amount of residue.

(Anticorrosivity)

The conditions of corrosion of copper film surface were observed andrated according to the following four stages:

⊚: There was no corrosion in copper film.

◯: There was slight corrosion in copper film.

Δ: There was corrosion in copper film.

X: There was striking corrosion in copper film.

(HSQ Damage)

The surface condition of HSQ film, when HSQ was used as a low dielectricfilm, was observed and rated according to the following four stages:

⊚: There was no damage.

◯: There was slight damage.

Δ: There was damage.

X: There was striking damage.

(MSQ Damage)

The surface condition of MSQ (methylated HSQ) film, when MSQ was used asa low dielectric film, was observed and rated according to the followingfour stages:

⊚: There was no damage.

◯: There was slight damage.

Δ: There was damage.

X: There was striking damage.

TABLE 1 Stripping solution composition Stripping Stripping Ratingsolution Anticorrosive agent Stripping Anticorrosivity HSQ MSQ No. agent(wt. %) (wt. %) Water performance to Cu damage damage 1 Uric acid NMAERemaining Δ Δ Δ Δ (1 × 10⁻⁵) (40) part 2 Uric acid NMAE Remaining Δ ∘ ΔΔ (1 × 10⁻⁴) (40) part 3 Uric acid NMAE Remaining ∘ ⊚ Δ Δ (0.01) (40)part 4 Uric acid NMAE Remaining ⊚ ⊚ ∘ ∘ (0.01) (80) part 5 Uric acidNMAE Remaining ⊚ ⊚ ⊚ ⊚ (1) (90) part 6 Uric acid NMAE Remaining ⊚ ⊚ ⊚ ⊚(1) (95) part 7 Uric acid MEA Remaining ⊚ ⊚ ∘ ∘ (1) (80) part 8 Uricacid MEA Remaining ⊚ Δ Δ Δ (1 × 10⁻⁴) (60) part 9 Uric acid MEARemaining Δ Δ Δ X (0.01) (40) part 10 Uric acid MEA Remaining ∘ Δ ∘ ∘(0.01) (80) part 11 Adenine NMAE Remaining ⊚ ⊚ ⊚ ⊚ (1) (90) part 12Caffeine NMAE Remaining ∘ Δ ⊚ ⊚ (90) part 13 Purine NMAE Remaining ⊚ ⊚ ⊚⊚ (1) (90) part 14 Pterin NMAE Remaining ⊚ ∘ ⊚ ⊚ (0.1) (90) part 15Cyanuric acid NMAE Remaining ⊚ ∘ ⊚ ⊚ (1) (90) part 16 Nicotinic acidNMAE Remaining ⊚ Δ ⊚ ⊚ (1) (90) part 17 BTA NMAE Remaining ⊚ ⊚ ⊚ ⊚ (1)(90) part *1: “Residue” in water amount refers to a residue when theamounts of anticorrosive agent and stripping agent have been subtractedfrom 100% by weight. *2: NMAE refers to N-methylaminoethanol. MEA refersto monoethanolamine. BTA refers to benztriazole.

From the above it is seen that the stripping composition of the presentinvention has excellent stripping performance and anticorrosivity.Incidentally, in the present Example, the present invention was appliedto a single damascene process; however, the present invention can beapplied also to a so-called dual damascene process.

EXAMPLE 2

A silicon wafer having a copper film formed on the whole substratesurface was immersed in a given stripping solution at 80° C. for 10minutes. The etching rate of copper was measured from the thicknesses ofthe copper films before and after immersion. As the stripping solution,there were used those having the following compositions. Incidentally,2N ammonia water was added to exclude the influence of the pH variationcaused by the difference in addition amount of uric acid, and pH wascontrolled at 11.

Amine: 80% by weight

Uric acid: 0, 0.0001, 0.001, 0.01, 0.1 or 1% by weight

Water: Remaining part

As the amine, NMAE (N-methylaminoethanol) was used. The results areshown in FIG. 3. When, in FIG. 3, the etching rate shown by the axis ofordinate exceeds 4 nm/min, corrosion of copper film becomes striking. Itis seen from FIG. 3 that excellent anti corrosivity is exhibited byaddition of uric acid.

EXAMPLE 3

The stripping components which had shown good results in Table 2, wereevaluated for biodegradabiliity according to a biodegradability testmethod based on the MITI method. That is, a sample was added to aninorganic medium so as to give a concentration of 100 mg/liter; anactivated sludge was added thereto; cultivation was conducted at 25° C.;amount of oxygen consumed and residual amount of sample were measuredusing a closed system oxygen consumption tester, to determine adecomposition ratio from the amount of oxygen consumed; andbiodegradability was judged according to the following rating standard.

⊚: Decomposition ratio was 60% or more.

◯: Decomposition ratio was 40% to less than 60%.

Δ: Decomposition ratio was 10% to less than 40%.

X: Decomposition ratio was less than 10%.

The results of rating are shown in Table 2.

TABLE 2 Sample Biodegradability Uric acid ⊚ Adenine ⊚ Caffeine ⊚ Pterin⊚ Cyanuric acid Δ Nicotinic acid ⊚ BTA X MEA ⊚ NMAE ⊚ BTA: benztriazoleMEA: monoethanolamine NMAE: N-methylaminoethanol

EXAMPLE 4

In this Example, stripping compositions according to the presentinvention were applied to a process for throughhole formation on acopper wiring. Ammonium fluoride having a strong stripping action wasused as a stripping component. Substantially the same process as inExample 1 was used; however, since the thickness of nitride film and thekind of etching gas were slightly different, each deposit to be strippedwas different from those of Example 1. The results of rating are shownin the following table. The standards for rating of strippingperformance and anticorrosivity were the same as in Example 1. Thestripping compositions using uric acid showed about the same strippingperformance and anticorrosivity as a BTA derivative.

TABLE 3 Strip- Peeing solution composition Rating ping so- AnticorrosiveStripping lution agent perform- Corro- No. (wt %) Stripping componentance sivity 1 Uric acid DMSO (69), ⊚ Δ (0.01) ammonium fluoride (1),water (residue) 2 Uric acid (1) DMSO (68), ammonium ⊚ ∘ fluoride (1),water (residue) 3 Uric acid NMP (69), ammonium ∘ Δ (0.01) fluoride (1),water (residue) 4 BTA derivative DMSO (68), ammonium ⊚ ∘ (1) fluoride(1), water (residue) 5 None DMSO (69), ammonium ∘ X fluoride (1), water(residue) NMP: N-methyl-2-pyrrolidone DMSO: dimethyl sulfoxide

INDUSTRIAL APPLICABILITY

As described above, the stripping composition of the present inventioncontains a heterocyclic compound of particular structure as ananticorrosive agent. Therefore, the present stripping composition caneffectively remove a resist film and an etching residue while preventingcorrosion of copper, is superior in safety, and is biodegradable andeasy to treat its wastewater. Hence, the composition can be preferablyused in, for example, production of a semiconductor device having acopper wiring formed therein.

1. A stripping composition comprising (a) an anticorrosive agent, (b) analkanolamine and (c) water, wherein the anticorrosive agent (a) is areadily biodegradable heterocyclic compound having a nitrogenatom-containing six-membered ring.
 2. A stripping composition accordingto claim 1, wherein the alkanolamine (b) is readily biodegradable.
 3. Astripping composition according to claim 1, wherein the anticorrosiveagent (a) is a compound represented by the following general formula (1)

wherein A₁, A₂ and A₃ are each independently a hydrogen atom, a hydroxylgroup, an alkyl group having 1 to 5 carbon atoms or an amino group.
 4. Astripping composition according to claim 1, wherein the anticorrosiveagent is readily biodegradable purine or a derivative thereof.
 5. Astripping composition according to claim 1, wherein the anticorrosiveagent (a) is uric acid.
 6. A stripping composition according to claim 1,wherein the anticorrosive agent (a) is adenine.
 7. A strippingcomposition according to claim 1, wherein the alkanolamine is onecompound or two or more compounds selected from the group consisting ofmonoethanolamine, N-methylaminoethanol, 2-(2-aminoethoxyethanol),N-methyldiethanolamine and 1-amino-2-propanol.
 8. A strippingcomposition according to claim 1, wherein the components (a), (b) and(c) are contained in amounts of 0.0001 to 20% by weight, 1 to 95% byweight and 1 to 90% by weight, respectively.
 9. A stripping compositionaccording to claim 8, wherein the component (a) is contained in anamount of 0.001 to 1% by weight.
 10. A stripping method which comprisesremoving a resist film and/or an etching residue, present on asemiconductor wafer containing an exposed surface of a copper filmand/or a copper alloy film, using a stripping composition according toclaim 1.